Johnston, Francis (1760/61–1829), architect, was the second of two sons of William Johnston (1728–92) of Armagh, architect and builder, and his first wife, Margaret, daughter of James Houston. The family, originally from Scotland, settled in Ireland in the early seventeenth century with the arrival in Dromore, Co. Tyrone, of the Rev. Thomas Johnston. The subject's great-great-grandfather, William Johnston of Tyholland, Co. Monaghan, superintended the restoration of public buildings damaged during the rebellion of 1641. Nothing is known of Francis's early education, but he may have attended the Royal School, Armagh, which was under the patronage of the primate, Archbishop Richard Robinson (qv). In 1778 Robinson sent him to Dublin to become a pupil of his architect Thomas Cooley (qv), who also held the post of clerk and inspector of civil buildings in the barrack board. He remained with Cooley until 1782, when he entered the Dublin office of his own cousin, the architect and developer Samuel Sproule (qv), who built much of the east side of Merrion Square. After Cooley's death (1784), Johnston took his place as Robinson's architect on building projects in Armagh and on his estates in Co. Louth. Johnston was based in Louth for the next decade, residing in or near the town of Drogheda and at Robinson's country house, Rokeby Hall, Dunleer, which he apparently completed from Cooley's designs. Nearby, in the rural parish of Ballymackenny, Robinson employed Johnston to erect a church from earlier designs by Cooley. In Drogheda he designed the cornmarket (1787, begun 1796) and a spire for the parish church of St Peter (c.1785) as well as a new catholic church (1791, replaced in 1884) and the Sienna convent (1792).
In 1791 Johnston married, in Dublin, his cousin Anne Barnes, whose sister Susanna had married his elder brother Richard (1759–1806) in 1789. After Robinson's death (1794), Johnston moved to Dublin, where Richard was already established in independent architectural practice and as a property developer. He acquired a house in Eccles St. (later extended), part of a development commenced by Richard in 1793. There were no children of either marriage, the Johnston line being eventually continued by the offspring of a younger brother, Andrew, a Dublin surgeon, one of two sons of William Johnston's second marriage. Francis and Anne Johnston remained in Eccles St. for over thirty years. He built a Gothic campanile behind the house but later moved the bells to St George's church after his neighbours complained. In 1822 he and his brother Andrew built a block of four houses (since demolished) on the north side of Eccles St.
In March and April 1796 Johnston made a tour of England and Wales, which he recorded in a diary. His study of medieval architecture there was to provide sources for much of his subsequent Gothic-revival work. His country houses in that style included Charleville Forest (1800–12), King's Co. (Offaly); Markree Castle (1802–5), Co. Sligo; and the enlargement (1802–13) of Killeen Castle, Co. Meath. However, Johnston's greatest aesthetic achievement of this period was arguably his handling of minimalist neo-classical detailing in Townley Hall (1794–6), Co. Louth, the seat of Blayney Townley Balfour. This building can be seen as the apogee of a style brought back from Italy in the 1750s by Cooley's own master, Robert Mylne (1734–1811). This was followed in the early 1800s by major classical work in Dublin including St George's church, Hardwicke Place (1800–14), and the remodelling of the parliament house for the Bank of Ireland (1803–8).
In 1805 Johnston embarked on a career in the public service when he succeeded Robert Woodgate as architect to the board of works, although he did not entirely give up private practice. He worked on several of Dublin's major public buildings, including the Gothic-revival Chapel Royal at Dublin Castle and the adjacent, reconstructed Record Tower (1807–14), and improvements to the adjoining state apartments. The Chapel Royal was a seminal building of the Gothic revival; with forms and details based on historic precedent and a wealth of stone and wood carving, it presaged the scholarly Gothic of the Victorian era. It also played homage to its earlier Gothic-revival neighbour, the reconstructed Birmingham Tower (1775–7) at the opposite end of the state apartments, attributable to his master Cooley and Christopher Myers. Other works in Dublin by Johnston were the General Post Office (1814–18); its neighbour, Nelson Pillar (1808–9, demolished 1966), where he was executant architect for William Wilkins's design; and the viceregal lodge (later Arás an Uachtárain) where he added the north (1808) and south (1815) porticos. In 1804 he succeeded Vincent Waldré as architect to the Royal Hospital, Kilmainham, which he modernised. At the foot of Watling St., on the eastern approach to the hospital, he constructed (c.1808) a substantial Gothic gate tower (moved to the west end of the hospital grounds in 1846/7). He was probably also the architect of the neo-Grecian adjutant-general's house in the hospital grounds. Johnston also designed a number of Dublin hospitals, including the Richmond Lunatic Asylum (1810–15, reconstructed and reopened in 2021 as part of TU Dublin campus), extensions to the two Dublin workhouses, and two prisons: the Richmond Penitentiary (1812–16), Grangegorman, and the Richmond Bridewell (1813–18), South Circular Road. He was assisted in his later career by his cousin and partner William Murray (1789–1849). Murray served with him as joint architect to the board of works from 1822 to 1826, when Johnston retired.
Johnston and Murray also acted for the government in approving designs furnished for local prisons by consultant architects. In 1817, following a limited competition with the English architect James Bevans, Johnston was appointed to design a number of district asylums to be erected by a new board of control. Four were built by him and Murray between 1821 and 1829, and a further five were completed by Murray by 1835; all two-storey in a classical style with a central cupola, but with variations in detail and accommodation. There were two basic plan types; the larger employed at Ballinasloe and Limerick, the smaller at Armagh, Belfast, Derry, Carlow, Maryborough (Port Laoise), Waterford, and Clonmel.
Johnston was one of the promoters of the new Royal Hibernian Academy, which was granted a charter of incorporation in 1821. He was eventually to donate £14,000 to it for the construction of a new building on Abbey St., built from his designs (burnt out in 1916). He was president of the academy from 1824 until his death on 14 March 1829. He was buried in a simple grave, said to have been his own design, in the burial ground of St George's parish. His wife survived him until 1841.